The invention concerns a thermally triggered safety device to automatically shut off the fluid in pipelines, especially gas pipelines, in case of impermissible temperature rises, according to the conception of the species of the 1.sup.st patent claim.
Thermally triggered safety devices as mounted on pipelines, for example, upstream to gas fittings, gas appliances, gas meters, etc., are found in a great number of different designs. They all serve to shut off the gas in case of rising temperature well before the temperature at such gas fitting, appliance, or meter, may become high enough to jeopardize its tightness against the environment.
One of such thermally triggered safety device, as described above, is specified in DE 44 22 241 A1. In this solution, a closing body, situated inside the casing in axial direction opposite to an in-built seat, is kept in open position by one or more nearly U-shaped structural parts. To serve as such, the closing body has--right behind the sealing face which is directed towards the seat--a necking on the closing body's side opposite to the seat, followed by a collar of preferably cylindrical shape. The two limbs of the U-shaped part are located around the necking, in this way supporting the collar to withstand the forces exercised by the closing spring. Furthermore, the U-shaped part's section that connects the two limbs rests on a fusible soft solder component which in turn rests on the inner surface of the casing wall. If said fusible soft solder component melts off, the U-shaped part's limbs--as they move out of their original position relative to the casing--are no longer located around the closing body's necking so that the latter is allowed to being pushed by the closing spring into its close position. At the same time, the two limbs are forming a slide-way to guide the collar and/or the sealing face of the losing body towards the seat.
The above solution's disadvantage is the fact that--in addition to the closing body itself--there is a lot of other things built in the casing, in most cases being situated within the closing body flow cross--section. In order to achieve the flow rates specified in standards, or desired in praxi, you have to determine the fitting size correspondingly. This, in turn, entails noncompliance with other--required and/or desired--fitting sizes.
Also known from EP--PS 605 551 is a so-called "fire valve", equipped with a closing spring, to be mounted on pipelines as an automatic shut-off device. Inside this fire valve, in a separate casing, there is a metal closing body, with a ball-shaped sealing face, which--in open position, under the force exercised by a closing spring--rests on three fix points formed by two balls and one temperature-sensitive structural part. The two balls, which in turn rest on a shoulder situated inside the casing, are located in such a distance to each other to form an approach angle of approx. 90 degrees. Opposite to this approach angle, fixed to the inside wall of the casing, there is the temperature-sensitive structural part.
The latter comprises an inward open tray, the bottom of which is fixed to the inner wall. A fusible soft solder component is placed inside the inward radially open tray into which is pressed a ball that snugly fits to the tray's opening, in this way forming the third fix point, and--in case of no longer existing fusible soft solder component--would be nearly completely taken up by the tray. The diameter of the area of support formed by these three fix points is calculated so that the closing body, with the ball being taken up by the tray, will be pushed under the force exercised by the spring through the enlarged opening formed by the three fix points.
As can be clearly seen from the corresponding FIG. N.degree. 1, the disadvantage of this solution is the fact that the closing body, resting in an open out-of-center position, is not axially guided when moving into its close position. Due to existing tolerances the forces of closing spring will never be acting perfectly in axial direction and, therefore, lateral excursions of the ball occur when it moves into its close position. This naturally leads to a lateral impact, requiring an extra movement to be seated into center position, that consumes part of the kinetic energy which is needed to achieve a proper press fit. Such press fit, however, is required in any case to make sure that the thermally triggered safety device will be effective even at temperatures at which the closing spring will already have lost its pressing power.
The invention focuses on the problem of developing a thermally triggered safety device as described above, which makes sure that the closing body is axially guided when moving into its close position. In addition, said thermally triggered safety device should have a largely undisturbed ring cross-section. Also, production cost and fitting size should be kept at a minimum.
According to the invention, the problem is solved by arranging three or more solid ribs inside the casing in such a way that their longitudinal axes are parallel to the direction of the closing body's movement into close position so that each of these ribs form a slide-way to guide the closing body in its movement from open into close position. Also, a first groove is cut into these ribs to take up a shaped part on which the closing spring rests. At least the ribs arranged approximately opposite to the tappet have a second groove, whose seat-facing side forms a rest edge for the control edge at the closing body in its open position. If the fusible soft solder component melts off, the tappet changes its position in axial direction under the force exercised by the closing spring. Due to the change in the tappet's position, the control edge is no longer sitting dose to the rest edge, and the closing body, driven by the closing spring's action, moves into its close position.
The above solution, hence, removes the prior art's disadvantages, i.e. firstly, there were too many things, besides the closing body, built in the casing, in most cases situated even within the closing body flow cross-section, and secondly, the closing movements were not perfectly axial. In addition, this solution is distinguished above all by its simplicity and small fitting size, the latter being of special interest with greater nominal widths.
Other advantageous features of the invention are defined in the patent claims. The rest edge, for example, may be integrated into the first groove's lateral edge that faces the seat so that the manufacturing costs can be minimized further, and/or the tappet may rest in one of the solid ribs, etc.
In order to have an optimum flow cross-section design, it is advisable to make the solid ribs from section rods supported both around the seat and near the casing's entrance area.
Manufacturing-wise, it is particularly advantageous to form the solid ribs from fins which are connected with the casing in form of a single-piece casting.
To simplify assembling activities, above all, the shaped part may be designed in such a way that it can be twisted inside the groove, and an individual curved path located on said shaped part is assigned to each single rib. The minimum distance of this curved path to the shaped part's center is less than half the diameter created by the rib edges alongside the casing's longitudinal axis, whereas the maximum distance of this curved path to the shaped part's center nearly equals the distance between the groove's bottom and the casing's longitudinal axis. As an addition, a peg may be fixed in said distance to limit the curved path and the shaped body's twisting movement inside the groove, with the rib acting as a limit stop.